In the construction of concrete floors or surfaces (i.e. sidewalks, driveways, roads, etc.), it has long been the practice to make the surface from a series of individual blocks or slabs. Adjacent slabs meet each other at joints which are typically spaced so that each slab has enough strength to overcome internal stresses that would otherwise cause random stress relief cracks.
One problem that can arise when slabs are poured in separate subsections is that the junctions or joints between adjacent sections are subject to damage from downward forces exerted against the slab. To reduce the effects of such forces, it is common practice to embed dowels into the slab. The dowels bridge across the joint between adjacent subsections of the slab and extend a short distance into each subsection. The dowels are placed at regular intervals along the joint, and act to equalize and transfer loads that are exerted against the joint. Various systems have been developed utilizing dowels of a variety of shapes and sizes, including generally planar plate-type dowels, as well as dowels having square, circular or other shaped cross-sections.
If the dowels are not installed correctly, problems can arise. Specifically, if the dowels are not parallel to the slab surface and perpendicular to the joint between the slab sections, unwanted stresses can be created in the slab, which can lead to cracking of the slab. A number of systems and methods have been developed to better ensure proper alignment of the dowels. In some systems dowels, or sheaths for supporting the dowels, are attached to forms prior to pouring of a concrete slab. For example, in U.S. Pat. No. 6,354,760, the disclosure of which is incorporated herein by reference in its entirety, a generally planar plate-type dowel is shown which is supported by a sheath that is embedded within one of two adjacent concrete slabs. The sheath is nailed to an inner surface of a wood form as a first slab is poured. Once the slab has properly hardened, the form is removed and the sheath remains. The dowel is then positioned in the sheath such that half of the dowel protrudes beyond the edge of the slab into a location that will be occupied by the adjacent slab. The adjacent slab is poured and the protruding portion of the dowel is surrounded by the concrete of the second slab.
The generally planar plate-type dowels discussed above provide several advantages over square and round tubular dowels such as increased relative movement between slabs in a direction parallel to the longitudinal axis of the joint; and reduced loadings per square inch close to the joint, while transferring loads between adjacent cast-in-place slabs. Nevertheless, current systems and methods utilizing planar plate-type dowels require that the dowel be installed in new concrete as it is poured. Alternatively, systems and methods have been developed in which a hole is drilled into pre-existing hardened concrete for insertion of a tubular dowel, allowing tubular dowels to be utilized in section repair or other retrofitting applications in which the concrete has been poured and set/hardened prior to placement of dowel (or sheath) within the slab. Notwithstanding the noted disadvantages of tubular dowels versus planar dowels, drilling in existing concrete is extremely time consuming and creates considerable dust which is undesirable for interior retrofit applications. Therefore, it would be beneficial to provide a system and method for utilizing planar dowels in connection with existing or retrofit concrete applications, and which is easier and less dusty than existing retrofit systems utilizing tubular dowels.
A disadvantage of prior art systems and methods of utilizing planar dowels in new concrete pours in which a sheath is embedded in a slab, is that only wooden forms can be used for forming the slab. This is because the sheath must be nailed to the form before the concrete is poured. Nevertheless, many contractors prefer to utilize reusable metal forms as opposed to wooden forms. Therefore, it would be beneficial to provide a system and method for utilizing planar dowels in slabs that are made with metal forms.
Utilization of the generally planar sheaths of the prior art for positioning dowels within a slab require vibration of the wet concrete to allow the concrete to consolidate around the sheath. When the adjacent slab is poured, the wet concrete for that slab must also be vibrated to allow the concrete to consolidate around the protruding portion of the dowel. Vibration of the wet concrete requires additional labor and special tools that are not necessary in applications in which generally narrow tubular dowels are utilized. Therefore it would be beneficial to provide a system and method for utilizing planar dowels in slabs that reduces the labor required during pouring.
Another disadvantage of prior art systems for locating planar dowels in a slab is that attachment of the sheath to the form requires extremely careful positioning of the sheath with respect to the top edge of the form as well as extremely careful leveling of the form at the location in which the slab edge is to be made. Even slight misalignment of either the sheath or of the form board will result in misalignment of the dowel with the slab and can result in undesired stresses in the slab. Misalignment or dislocation of the sheaths can result after the sheath has been mounted to the form either as the form is being positioned or after the form is in position by workers accidentally stepping on the sheaths or bumping against the sheaths. Misalignment of the form board can also result from workers accidentally kicking the form board, or misalignment can be the result of a warped form board. Therefore, it would be beneficial to provide a system and method for ensuring proper alignment of planar dowels in slabs.